Process for treating phosphate rock



EARL P. STEVENSON, OF NEWTON, MASSACHUSETTS.

PROCESS FOR TREATING PHOSPHATE ROCK,

No Drawing.

Toallwlwmz'trmag concern: i

Be it known that I, EARL R S'rnvaNsoN, a citizen of the United States,residing at Newton, in the county of Middlesex, and

State of Massachusettsphave invented. c'er-' tain new and usefulImprovements in Processes for Treating Phosphate Rock; and I do herebydeclare the following to be a full,

clear, and exact description of the invention, such as will enableothers-skilled in-the art a to which it appertains tomake and use thesame.

The present invention relates to methods I of treating crude pebblephosphate to in crease the bone phosphate of limecontent and is acontinuation in part of my earlier application filed August 14, 1920,Serial No..403,544.. I

-The crude pebble phosphates such as occur naturally in'Florida have ingeneral a bone phosphate of lime content averaging below seventy-fourper cent. The hard phosphate rocks which may contain a substantiallyhigher percentage of bone phosphate of lime averaging above seventy-fourper cent are accorded a difierent' classifica-- 1 phosphate of limecontent, however, may be .free lime substantiall increased; if therock-is subjected to ca cining at highertemperature to break up thecalcluni carbonate present into carbon dioxide and free lime.. Unlessthe however, e increase of bone phosphate of lime is not rmanent,- dueto the tendency of the free ime to recombine with carbon dioxide fromthe air reformingv calcium carbonate. esses have attempted to secure apermanent increase in the bone pho'sphatefof lime content by heating thephosphate rock to a te m perature which will cause a combination ofthefree lime with silica which may be either present in the rock or addedthereto. This combination of the free lime with silica forms a silicateand permanently fixes the produced by this heating is fixed,- t

Accordingly, certain prior proc- Application filed January 15, 1921.Serial No. 437,579.

lime. This. method of disposing of the .free lime although'it doesresult in a permanent increasein the bone phosphate of lime content hascertain disadvantages which seriously militate against the use of theprocess;

Perhaps the most serious of these disadvantages 1s due to the fact thatthe sintered product produced as the result of the reac- I tion betweenthe lime and silica forms a sticky product when the commercial phosphate1s later treated to make it available for fertilizing purposes. Inaddition the completion of the reaction between the silica and the limerequires-a heating of the phosphate rock to a temperature of 2500 F.approximately which necessarily involves the expenditure of alargeamount of fuel with its attendant expense.

I have discovered that it is possible to'secure a permanent increase inthe bone phosphate of lime content by heating the crude pebblephosphate-containing calcium carbonate to temperatures ranging from 1800- F. to 200091 approximately, in order to break -up the calciumcarbonate into carbon diox ide and 'free lime with a subsequentrecombination of the free line to form a basic phosphate; The operationof this process'results in a permanent increase in the bone phosphateioflime content and in addition yields f 3 a non-sintered product whichlends itself readily to further treatment'forfthe production of'afertilizing material.

An actual example of crude pebble phosphate which may Ice-advantageouslytreated by my new process contains tricalcium phosphate, calciumcarbonate, moisture and organicjmatter in substantially the followingproportions:

Tricalcium phosphate 71.02% Calcium .carbonate..- 5.10% Moisture 0.69%Organic matter- 1.9 3%

ganic matter are driven ofi together with.

4 Upon heating this rock the moisture and orcarbon dioxide gas which isevolved as the result of the decomposition of calcium carbonate.Thereafter the Y tricalcium phosphate. undergoes a slight decompositioninto basic phosphate an approximate formula of which is expressed asfollows:

, v YC3 Q[C% Jeil and phosphoric anhydride the latter combining with the'free lime to form abasic 2 phosphate, this reaction being substantiallycomplete at a temperature of 2000? F. or

carbon dioxide.

.and a less. This process secures the maximum permanent increase in thebone phosphate of ime content by eliminating substantially all of thevolatile constituents from the crude pebble phosphate and fixes the freelime. to prevent a subsequent recombination with Furthermore the productresulting from the process is a friable material which may be readilyhandled and.

"when this material is converted for fertilizingpurposes a stickyobjectionable product A is formed. v

lit will be obvious to. those skilled in the art that my new process hascertain distinct advantages due to .the reduced temperature at which thereaction takes place and the improved product which is obtained. Theprocess is furthermore free from the objectionable features of priorprocesses which require substantially higher temperatures and which havecertain disadvantages due to the inherent characteristics of thereaction.

I claim l. A process for treating pebble phosphate initially containingtricalcium phosphate, calcium carbonate, moisture and organic matter,which consists in heating the crudephosphate withoutaddition of othermaterials, to a temperature not over 2,000 degrees Fahrenheitapproximately to decompose the calcium carbonate and cause asubstantially complete conversion of the free lime resulting from thedecomposition of the calcium carbonate, as phosphate.

2. The process of treating pebble phosphate which consists in heatingthe crude pebble phosphate to a temperature of 1,800 I to 2,000 degreesFahrenheit approximately to decompose the calcium carbonate into freelime and carbon dioxide and partially dissociate the tricalciumphosphate, the products of dissociation combining with the free lime atthese temperatures in a manner to permanently fix the latter.

3. A process for increasing the phosphate content in pebble phosphatewhich consists in calcining the rock at a temperature sufficiently highto cause the conversion of the calcium carbonate present in the rockinto additional phosphate.

EAR-L 1. STEVENSON.

